In a communications network, direction of communications are typically described as being either upstream or downstream relative to a fixed point in the communications network. For example, communications toward a central office from a subscriber terminal is described as upstream communications, while communications away from the central office toward the subscriber terminal is described as downstream communications. In a communications network, there are often more than one subscriber terminal communicating upstream. An aberrant situation arises if the upstream communications of one subscriber terminal interferes with the upstream communications of another subscriber terminal. In a large communications network, one having many subscriber terminals communicating upstream, it can be difficult to determine which subscriber terminal is causing the aberrant situation.